The networking of control units, sensor systems and actuator systems with the aid of a communications system and a bus system, thus a communications link, has increased dramatically in recent years in the construction of modern motor vehicles or also in machine construction, especially in the field of machine tools, thus in automation, as well. In this context, synergistic effects may be achieved by the distribution of functions to a plurality of control units. These are called distributed systems. The communication between different stations is taking place more and more via a bus system, thus a communications system. Communication traffic on the bus system, access and reception mechanisms, as well as error handling are regulated by a protocol. One conventional protocol for this purpose is the CAN protocol or also the TTCAN protocol, as well as the FlexRay protocol, the FlexRay protocol specification V2.0 presently being the basis. The FlexRay is a rapid, deterministic and fault-tolerant bus system, particularly for use in a motor vehicle. The FlexRay protocol operates according to the method of Time Division Multiple Access (TDMA), in which the components, thus the users or the messages to be transmitted, are assigned fixed time slots in which they have an exclusive access to the communications link. This is comparably implemented in the case of the TTCAN, as well. In this context, the time slots repeat in a fixed cycle, so that the instant at which a message is transmitted via the bus can be predicted exactly, and the bus access takes place deterministically. To optimally utilize the bandwidth for the message transmission on the bus system, the FlexRay subdivides the cycle into a static and a dynamic portion. The fixed time slots are in the static portion at the beginning of a bus cycle. In the dynamic portion, the time slots are assigned dynamically. Therein, the exclusive bus access is now in each case permitted for only a brief time, so-called minislots. The time slot is lengthened by the necessary time only if a bus access takes place within a minislot. Consequently, bandwidth is used up only if it is also actually needed. FlexRay communicates via two physically separate lines with a data rate of a maximum of 10 MB per second each. The two channels correspond to the physical layer, in particular of the OSI (open system architecture) layer model. They are now used chiefly for the redundant and therefore fault-tolerant transmission of messages, but can also transmit different messages, whereby the data rate would then double. However, FlexRay can also be operated with lower data rates.
To realize synchronous functions and to optimize the bandwidth by small spacings between two messages, the distributed components in the communication network, thus the users, need a common time base, the so-called global time. For the clock synchronization, synchronization messages are transmitted in the static portion of the cycle, the local clock time of a component being corrected with the aid of a special algorithm according to the FlexRay specification in such a way that all local clocks run synchronously with respect to one global clock. This synchronization is accomplished comparably in a TTCAN network, as well.
A FlexRay network node or FlexRay user or host contains a user processor, thus the host processor, a FlexRay controller or communication controller, as well as a bus guardian in the case of bus monitoring. In this context, the host processor, thus the user processor, furnishes and processes the data, which are transmitted via the FlexRay communication controller. Messages or message objects can be configured with, e.g., up to 254 data bytes for the communication in a FlexRay network. To now transmit these messages or message objects between the physical layer, i.e., the communications link, and the host processor, a communications module, in particular, a communication controller, is used.
The object of the present invention is now to control the data transmission in such a way that data integrity is ensured, and the transmission rate is optimized.